Why does my cycles preview cause my PC to freeze
It seems like your CPU/GPU can't handle the cycles render.
Cycles samples the scene as fast as it can, I think your computer freezes while trying to sample the scene:
 (You can find this at the top of the 3D view.)
I suggest trying a simple scene and see if that stops freezing the scene. If it doesn't, I believe there is a problem with your CPU/GPU or it is not supported for Cycles.
It may just be a problem with selecting the wrong computing device. If you have a supported GPU you can select it like me under User Pref &gt; System:

And then selecting GPU under the rendering tab:

And if that still doesn't work, try selecting the CPU instead.
And if all that fails, I recommend getting a better GPU/CPU. You can compare and find the best one for your price here: http://olivieramrein.com/2012/02/25/blender-cycles-best-hardware-using-the-benchmark-spreadsheet-analysis/